Coaxial Cable

Overview

Coaxial cable carries the signal on a centre conductor surrounded by a braided or foil shield, with a dielectric holding the two at a constant spacing. That geometry gives it a defined characteristic impedance, most commonly 50 ohms, and makes it immune to the pick-up that affects unbalanced open wire.

The trade-off is loss. Coax dissipates a proportion of the power travelling along it, and that loss rises with frequency and with cable length. Thin cable is convenient and lossy; thick cable is awkward and efficient. Choosing a cable is really a question of how much loss you are willing to accept at your highest operating frequency.

Bands and modes

Band coverage

Modes

Safety note

Using it well

• Size the cable for the highest frequency you actually operate, not the lowest.
• Weatherproof every outdoor connector with self-amalgamating tape and a drip loop.
• Keep the run as short as the layout allows — every extra metre costs signal.
• Check the shield for corrosion annually; water ingress ruins cable from the inside.